1. Field of the Invention
The present invention relates to a spin field effect transistor, in particular to an all-electric spin field effect transistors.
2. Description of the Related Art
The spin field effect transistor (Spin FET) is a concept proposed by Supriyo Datta and Biswajit A. Das in the journal of Appl. Phys. Lett. 56, 665 (1990) at the earliest time. In the proposed structure thereof, the source electrode and the drain electrode act as an injection node and a detection node respectively for the spinning electrons by adopting ferromagnetic materials. When the bias voltage of the gate is 0, the spinning electrons from the injection node may arrive the detection node through the passage of two-dimensional electron gas (2DEG) formed by semiconductor heterojunction; when the bias voltage of the gate is not 0, the electric field in the passage will undergo changes (such as the electric field perpendicular to the direction of the passage increases or decreases). At this time, these changes of the electric field will also change the equivalent magnetic field which affects the moving electrons (Rashba effect) and thus affects the precession speed of spin for electrons. It is also equivalent that the direction of the electron spin may be controlled by the magnitude of the applied external electric field, thereby affecting whether the electron spin current passes through or not (based on the angle difference between the spin and the detection node, passing through if parallel and not passing through if antiparallel).
However, the spin injection efficiency of ferromagnetic materials and semiconductor heterojunction is currently very low, and an applied external magnetic field is required to change the direction of spin polarization for the injection node and the detection node. In addition, the factors such as the spin lifetime of the electron spin and the phase spread of the electron spin are also great problems to realize the spin field effect transistors.